Method of and material for treating ferriferous metal surfaces with manganese phosphate coating solutions



Patented July 25, 1950 FERRIFEROUS SURFACES WITH MANGANESE PHOSPHATE COATING S LUTIJONS Josep h Maz'ia; Philadelphia, Pa, 'assignor to American Chemical Paint-Company, Ambler,

'NoDrawing'; Application-December 8, 1948 Serial No. 64,247

7 Claims.

This invention' relates to the phosphate coating art and'particularly to that art as applied to the-treatment of ferriferoussuriaces where a manganese phosphate coating solution is employed; Of course, the basic principles of phos betreated in any one of a number-of ways, i. e;,

by dippingthe Workinto the-solution or by flowing or spraying the solution over the surface. This requires that the-coating=-=bath or solution contain a certain minimum quantity of -free acid. If r the I acidity" be reduced,==th'e solutionbecomes so supersaturated with respect to the metallic phosphate that somep't the phosphate is-precip'itated as a solidiphase. This-precipitation (actually a mere crystallization of-aconstituent from a supersaturated solution) is'commonly :known as sludging out. Heretofore such sludging out has constituted: a major problem to-the users of these processes and materials and the present invention is particularly directed toward a' solution I of this problem.

The principal objects-of the present invention are'to provide a method ofas well-as a material for use in the treatment of ferriferous metals with manganese pho'sphate coating solutions whereby so-called"sludging out is substantially I eliminated or at least so greatly minimized or inhibited as to render the problemofdisriosing of the sludge-of n'o'sefious consequence; other object 'is to provide a m'anganese phosphate coating solution which has i a much greater degree of stability than coating solutions now commonly "in use, as well as to provide acornposition-or'material from which the bath or solution may-be prepared" or maintained in -proper workingcondition. Another object is tapro- ,vide a. concentrated composition or "material which can be utilized -by'-simple*"dilutionwith water. Still another objectis to provide a method of and material for u'se in manganese phosphate coating operations'by "means of which 2a.,acorporaitiohof Delaware U 2; any substantial "incrustation or build-up of deposit on the heating surfaces is avoided or at least greatly-minimized which, of course, makes it easier to maintain a unifdrm bath temperature and aids in reducing maintenance costs.

Before proceeding with a detailed description of the present invention .1 wish to define'sta ibility as employed vherein. 'Thisrefers to the .degree at!) Whichanacid phosphate solution of the character described resists-spontaneous disturbancecfits state of acidity, (or its pH). Asis well known in this art, where supersaturated acid phosphate coating solutions are employed, there'is a"tenden1cyfor'thesolutions to increase in .a'cidity'. 'Ifherefore', increase in acidity accompanies a loss in supersaturation and the loss in supersaturation is evidenced by the sludging out already referred to. This, of course, is accompaniedby a decrease in the pH of'the solution.

The present invention is based upon the discovery' thatthe addition of certain 'tartrate ions to an otherwise conventionally formulated man- .ganese phosphate coating bath imparts to the batha very greatdegree of stability and makes it possible to operate such'baths in a relatively sludge. freev condition for long periods of time. This,*of course; results iina .much more economical process because thebath does-not lose excessive quantities. oi -the actual coating-producing ingredients in thesludge forming phenomenon. j

With the exception of the ions of meso' tartaric ,acidrth'e tartrate ions may be introduced in any ,iorm desired as long as duejregard tosolubility and chemical'compatib'iliity of the compound are considered. For example, they may be int-roducedas potassium acid tartrate (cream of tartar). I prefer to use cream of tartar ina's- -much as-the addition 0f -this material has little effect on the pH of the ordinary coating bath. If tartaric acid -'is "used as a source of the tartratefion; thenenough neutralizing material such as caustic alkali, manganese carbonate, etc., must'be-added to the bath to adiustthe pHof the bath to ring it back within proper operating coating "range! Contrariwise; if Rochelle salts are used; a'suitable acid such as phosphoric acid mustbeaddedto the'bath to adjustthestarting pl-I. Such'adjustments in the degree" of acidity are expedients familiar to those skilled in the art of phosphate coating.

In order to bring out more fully the nature of the present invention, the following illustrative examples are given. For instance a concentrated composition may be prepared as follows:

out the tartrate will form copious quantities of sludge during heating and breaking in as well as in regular service.

The potassium permanganate and the iron filings of the above formula are introduced for reasons familiar to those skilled in this art. For instance, the potassium permanganate will oxidize a portion of the ferrous iron to yield a small quantity of the substantially insoluble ferric phosphatewhich latter tends to inhibit hydrolysis in accordance with the teachings of U. S. Patent 2,316,810. The iron filings also aid in the break- Formula I Manganese carbonate, 85% grams 200 Phosphoric acid, 75% do 550 Cream of tartar (potassium bitartrate) do 20 Water, to make liters 1 The foregoing formula produces a concentrated material which can be prepared for use by simple dilution with water and it will be noticed that the ratio of tartrate ion, calculated as tartaric acid, to manganese equals 0.196. In preparing a working bath or solution 10% by volume of the foregoin concentrate is employed.

Such a bath shows no sludging out even at the boiling point and produces excellent coat:- ings on ferriferous metal surfaces. If .the bath be prepared from the same concentrate minus only the cream of tartar, a very definite cloud point is reached at about 150 F., the cloud point being the point where sludging out" becomes evident. At higher temperatures sludge formation becomes heavy.

Formula II Manganese carbonate, 85% grams 193 Phosphoric acid, 75% do 546 Sodium nitrate do 61 Sodium bitartrate, monohydrate do 18.5 Water, to make liters 1 The foregoing formula yields another concentrated composition or material which, as beprepared from a concentrate containing no sodium bitartrate, developed a cloud point at approximately 150 F. with heavy sludge formation at higher temperatures.

Another concentrated formula which gives excellent results is the following:

. Formula III Manganese carbonate, 85% pounds 1.6225 Phosphoric acid, 75% gallons 0.3489 Potassium permanganate pounds 0.0003 Iron filings do 0.0406 Potassium bitartrate do 0.2080 Water, to make gallons 1 This yields a ratio of tartrate ion, calculated as tartaric acid, to manganese of 0.2525 and a bath containing 10% by volume in water may be prepared and heated gradually to an operating temperature of approximately 205 F. It is then broken in in the normal fashion familiar in this art by allowing it to act on metallic iron. This bathwill produce heavy corrosion retardant phosphate coatings in, customary periods of treatment, which coatings are useful also as antifriction surfaces of the nature familiar to those skilled in this art. The bath functions practically without sludging, whereas an identical bath withing in of the solution. However, I wish it to be distinctly understood that neither of these materials is in any way essential to a realization of invention.

In all of the foregoing formulas the preferable operating temperature is under the boiling point and preferably in the neighborhood of 205 F. as just indicated in connection with Formula III.

It will be noted from the foregoing that relatively very small amounts of tartrate ion in the bath have a stabilizing effect, but I have found that the beneficial effects of my invention can be secured within a rather wide range of tartrate ion. Experience has shown that best results are secured by operating with baths which contain from 0.5 gram per liter to approximately 15 grams per liter of the tartrate ion expressed as dextro tartaric acid. Below a concentration of 0.5 gram per liter the tartrate ion has a reduced stabilizing effect and as the concentration nears 15 grams per liter the coatings, on certain types of surfaces, may exhibit a lackof continuity, and when the tartrate ion exceeds 15 grams per liter, the phosphate coating may have a white precipitate formed thereon, which, for some uses, may beobjectionable.

Expressed in terms of the relationship between the tartrate ion and the manganese, I have found that the ratio of tartrate ion (calculated as dextro tartari acid) to manganese should lie between approximately 0.03 and 1.5.

In conclusion I should like to point out that it is well known in this art that the lower the temperature of the manganese phosphate coat- .ing bath, other things being equal, the higher must be the pH. ,At any given temperature there exists a pH corresponding to the equilibrium of the solution with the particular solid phosphate. At a higher pH the solution is supersaturated and tends to form sludge with the liberation of acid in the solution. Operating baths at or above the pH of equilibrium is common practice in this art. In any case, theaction of the solution on the metal to be coated consumes acid and raises the pH in the neighborhood of the metal. This action is quite normal and necessary to cause the deposition of the desired coating. Usually, however, in the practice of the prior art, not all the solid phosphate deposited remains upon the metal surface as a coating. Some remains loose in the solution and formsa sludge. However, by

using tartrate ion in accordance with my invention it is possible to operate at a higher pH than it otherwise would be without an increase in the formation of sludge which, of course, may be a distinct advantage in certain situations. For instance, by operating at a higher pH, it is sometimes possible to lower the operating temperature of the bath.

.well as from dextroelevo (racemic) acid will function satisfactorily in accordance with the teachings of this invention, whereas, ions from meso tartaric acid will not so function. Just why this is, I do not know, but in the following claims I have excluded the ions of meso tartaric acid. Broadly speaking ions from the other acids may be used in whatever quantity is necessaryi to have a stabilizing effect suflicient to be of value in this art and they can be used in any manganese phosphate coating bath consisting of coating-producing proportions of the ions of phosphoric acid and of manganese.

I claim:

1. In the art of treating ferriferousmetal surfaces with a manganese phosphate coating bath, the method which consists in preparing an acid manganese phosphate bath containing the ions of a tartaric acid other than mesotartaric acid in quantity suflicient to substantially inhibit "sludging out" of metallic phosphate, and treating the surface with the bath to form the desired coating.

2. The method of claim 1 in which the bath contains from 0.5 to 15 grams per liter of tartrate ions calculated as tartaric acid.

3. A substantially supersaturated acid manganese phosphate coating bath containing from 0.5 to 15 grams per liter of tartrate ions other than the ions of mesotartaric acid calculated as tartaric acid.

4. In the art of treating ferriferous metal surfaces with an acid manganese. phosphate coating bath, a composition for preparing or replenishing the coating bath consisting essentially of materials capable of yielding manganese ions and phosphate ions and a compound capable of yielding tartrate ions other than those of mesotartaric acid, the amount of said compound being sutilcient to yield in the finished bath enough .0!

said tartrate ions to substantially inhibit the formation of sludge.

5. In the art of treating ferriferous metal surfaces with an acid manganese phosphate coating bath, a composition for.v preparing or replenishing the bath upon mixture with water, said composition consisting essentially of ingredients capable of yielding, in the bath, the desired coating-producing proportions of the ions of phosphoric acid and manganese together with a material yielding tartrate ions other than the ions of mesotartaric acid, in a ratio of tartrate ion (calculated as tartaric acid) to manganese of from 0.03 to 1.5.

6. In the art of treating ferriferous metal surfaces with an acid maganese phosphate coating bath, a concentrated, water-dilutable solution consisting essentially of manganese phosphate coating ingredients capable of yielding, in the bath. the desired coating-producing proportions of the ions of phosphoric acid and manganese together with a compound capable of yielding tartrate ions other than those of mesotartaric acid in a ratio of tartrate ion (calculated as tartaric acid) to manganese of from 0.03 to 1.5.

7. A manganese phosphate coating bath consisting essentially of an acid manganese phosphate solution containing from 0.5 to 15 grams REFERENCES CITED The following references are of record in th file 0! this patent:

UNITED STATES PATENTS Name Date Jernstedt et a1 Oct. 5, 1943 Number 

1. IN THE ART OF TREATING FERRIFEROUS METAL SURFACES WITH A MANGANESE PHOSPHATE COATING BATH, THE METHOD WHICH CONSISTS IN PREPARING AN ACID MANGANESE PHOSPHATE BATH CONTAINING THE IONS OF A TARTARIC ACID OTHER THAN MESOTARTARIC ACID IN QUANTITY SUFFICIENT TO SUBSTANTIALLY INHIBIT "SLUDGING OUT" OF METALLIC PHOSPHATE, AND TREATING THE SURFACE WITH THE BATH TO FORM THE DESIRED COATING. 